This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Previous work has shown that DNA polymerase alpha (Pol1) is tightly regulated during the cell-cycle, and that altered levels of Pol1 can lead to checkpoint control dysfunction, reduced S-phase DNA damage repair, and genomic instability. These observations suggest that Pol1 may be heavily involved in DNA damage detection during replication, as well as checkpoint control. Very little is known about the role that post-translational modifications play in regulating Pol1 during the cell cycle or in response to DNA damage. A likely possibility is that Pol1 undergoes post-translational modification via ubiquitylation or SUMOylation. In support of this idea is the observation that Pol1 rapidly disappears during the metaphase-anaphase transition during mitosis, suggesting that Pol1 undergoes ubiquitylation that signals its degradation;however, the candidate ubiquitin ligase is currently unknown. Due to the fact that this field is relatively unstudied, we propose to use the yeast two-hybrid screen to help elucidate candidate yeast Pol1 binding partners that may be involved in the regulation of Pol1 during the cell-cycle or DNA damage response.